1. Field of the Invention
The present invention relates to ophthalmoscopy lens systems, particularly those which may be easily sterilized without component damage or optical degradation.
2. Description of Related Art
Various ophthalmoscopy lens systems have been developed for use in the diagnosis and treatment of the eye. Many of these lens systems, particularly indirect ophthalmoscopy lens systems which create a real aerial image of structures within the eye, include a contact lens element which is placed directly on a patient's cornea. One particular type of indirect ophthalmoscopy lens system is that used for vitreoretinal surgery. Such lens systems are described, for example, in U.S. Pat. No. 5,963,301 (which is hereby incorporated by reference). Such lens systems are typically exposed to various bodily fluids during use, and therefore must be sterilized prior to each use.
Sterilization of ophthalmoscopy lens systems can be difficult and time consuming. In fact, many ophthalmoscopy lens systems can only be sterilized by specialized, time-consuming sterilization techniques, many of which will not be effective for certain microorganisms and other infectious agents. By way of example, “prions” are proteinaceous infectious agents which can cause transmissible degenerative encephalopathies such as Creutzfeldt-Jakob disease (“CJD”—a variant of which is the human version of “Mad Cow disease”). Prions tend to be more resistant to steam sterilization than conventional agents and are resistant to most sterilants typically used for sterilizing ophthalmoscopy lens systems. Recently, it has been reported that prions are susceptible to conventional autoclaving followed by a strong bleach solution or a solution of sodium hydroxide. Such a sterilization process will denature the prions. However, standard autoclaving cannot be employed with conventional ophthalmoscopy lens systems, particularly vitreoretinal lens systems such as those described in U.S. Pat. No. 5,963,301. Not only will the environment and bleach solution damage the lens element and other components, but liquid will enter the air space between the contact lens element and the imaging lens.
For example, the high-temperature, high-pressure steam environment of an autoclave is deleterious to both the contact lens element as well as the imaging forming lens. More particularly, acrylic contact lens elements, as they are typically implemented, tend to quickly haze and otherwise become non-transparent after a few cycles within a steam autoclave sterilizer. Also, glass image forming lenses interact with the steam produced by an autoclave to form hard water surface spotting. These hard water surface spots accumulate over repeated autoclave cycles and eventually render the glass lens element incompatible with effective retinal imaging.
In addition, as previously indicated, prior ophthalmoscopy lens systems are susceptible to water damage when liquid enters the air space between the contact lens element and the imaging lens. Such ophthalmoscopy lens systems include those configured such that the contact lens element and the image forming lens are in a spaced-apart sealed arrangement wherein a sealed air space is provided between the contact lens and the image forming lens. Such a lens system is described in U.S. patent application Ser. No. 10/689,568 (which is hereby incorporated by reference). After a number of steam autoclave cycles, due to the porosity of the high-temperature polymer housing and sealing members used in their construction, water in both vapor and liquid form encroach into the sealed cavity between the contact lens element and the image forming lens. This water eventually settles in sufficient quantities on the internal surfaces of the lenses to render the lens assembly incompatible with effective retinal imaging. Once water has breached into the internal cavity and has condensed on the internal lens surfaces, the internal surfaces have to be cleaned and dried before the lens can be effectively applied again. Moreover, vitrectomy lenses of this type are not well suited for disassembly and cleaning, as they require special tools to facilitate these actions.
Accordingly, there is a need for an ophthalmoscopy lens system of suitable composition and structure which may be easily sterilized without component damage or optical degradation.